The topcoat paint for automobiles comprises aluminum paste, a hydrocarbon based solvent such as xylene, a hardener, etc. When the paint at a thickness of approximately 40 .mu.m is applied to the surface of the body of an automobile, the aluminum flaky powder having a large water-covering area (approximately half of its specific surface area) becomes evenly distributed within the paint layer. As such, not only does it maintain appropriate luster, but it also serves to protect the coating layer on the surface of the body of an automobile by sealing off the outside air. At that time, however, if the average particle size of flaky aluminum powder is 40 .mu.m or larger, the powder protrudes out of the painting layer, resulting in poor external appearance, and fails to serve as a protective layer. If the average particle size is 10 .mu.m or less, the external appearance after painting appears dark, and thus it is not preferable. Consequently, the average particle size of flaky aluminum powder for automobiles should be 10 .mu.m to 40 .mu.m. At the same time, it should have a water-covering area of 5,000cm.sup.2 /g or larger, and the aluminum flaky powder should be non-leafing in the solvent.
The conventional method of producing aluminum paste for topcoat of automobiles comprises as follows: placing the gas-atomized powders, balls, mineral spirits, etc. in a vessel; ball-milling the same to obtain an intermediate paste containing flaky aluminum powder; vacuum-drying or filtering the same, followed by adjusting the amount of solvent to obtain the final product of aluminum paste containing over 60 wt % of aluminum powder. The above conventional method of utilizing the gas-atomized powders, however, requires a melting furnace, a high-pressure gas system, a large chamber, and a sieving system. In addition, at the time of melting aluminum, a large supply of electricity is required, which in turn translates into high investment costs along with high production costs for the powder.